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Background Unveiling the diversity of plant strategies to acquire and use phosphorus (P) is crucial to understand factors promoting their coexistence in hyperdiverse P-impoverished communities within fire-prone landscapes such as in cerrado (South America), fynbos (South Africa) and kwongan (Australia). Scope We explore the diversity of P-acquisition strategies, highlighting one that has received little attention: acquisition of P following fires that temporarily enrich soil with P. This strategy is expressed by fire ephemerals as well as fast-resprouting perennial shrubs. A plant’s leaf manganese concentration ([Mn]) provides significant clues on P-acquisition strategies. High leaf [Mn] indicates carboxylate-releasing P-acquisition strategies, but other exudates may play the same role as carboxylates in P acquisition. Intermediate leaf [Mn] suggests facilitation of P acquisition by P-mobilising neighbours, through release of carboxylates or functionally similar compounds. Very low leaf [Mn] indicates that carboxylates play no immediate role in P acquisition. Release of phosphatases also represents a P-mining strategy, mobilising organic P. Some species may express multiple strategies, depending on time since germination or since fire, or on position in the landscape. In severely P-impoverished landscapes, photosynthetic P-use efficiency converges among species. Efficient species exhibit rapid rates of photosynthesis at low leaf P concentrations. A high P-remobilisation efficiency from senescing organs is another way to use P efficiently, as is extended longevity of plant organs. Conclusions Many P-acquisition strategies coexist in P-impoverished landscapes, but P-use strategies tend to converge. Common strategies of which we know little are those expressed by ephemeral or perennial species that are the first to respond after a fire. We surmise that carboxylate-releasing P-mobilising strategies are far more widespread than envisaged so far, and likely expressed by species that accumulate metals, exemplified by Mn, metalloids, such as selenium, fluorine, in the form of fluoroacetate, or silicon. Some carboxylate-releasing strategies are likely important to consider when restoring sites in biodiverse regions as well as in cropping systems on P-impoverished or strongly P-sorbing soils, because some species may only be able to establish themselves next to neighbours that mobilise P.

Background and aims In extremely low-phosphorus (P) environments, most Proteaceae exude carboxylates from cluster roots. These carboxylates mobilise inorganic P which leads to a relatively high leaf manganese concentration ([Mn]). However, we found that Adenanthos cygnorum (Proteaceae) in a low-P habitat did not invariably have a high leaf [Mn] in south-western Australia. We aimed to explore how A. cygnorum acquires P in severely P-impoverished habitats. Methods We determined soil P concentrations and leaf [Mn] of A. cygnorum growing within 1 m and more than 10 m away from other large Proteaceae. We also grew plants in a glasshouse to determine its root carboxylate exudation and rhizosheath phosphatase activity. Results Adenanthos cygnorum did not produce functional cluster roots. It depended on carboxylates released by a P-mobilising neighbour, Banksia attenuata (Proteaceae), to acquire P when growing in severely P-impoverished soil (− 1 dry soil). In slightly less P-impoverished soil (> 11 mg P kg− 1 dry soil), phosphatases released by A. cygnorum hydrolysed sufficient organic P that was relatively mobile. Conclusion The reliance on facilitation of P acquisition in A cygnorum depended strongly on location. We demonstrated the exudation of phosphatases, which mobilise inorganic P; this P was adequate for growth when there was sufficient organic P in soil. Facilitation of P acquisition by B. attenuata allowed A. cygnorum to extend its range into severely P-impoverished habitats where it cannot exist without facilitation. This knowledge provides a better understanding of the diversity of P-acquisition strategies in severely P-impoverished environments.

Plant species richness increases with declining soil phosphorus (P) availability, especially for Proteaceae in old infertile landscapes. This difference in richness might be attributed to faster diversification in lineages adapted to P-impoverished soils, i.e. species that possess specialised P-acquisition strategies, and have lower leaf P concentration ([P]) and higher seed [P]. Alternatively, a longer time for species accumulation might contribute to high species richness in low-P environments due to the geological stability of the landscapes in which they evolved. We assessed differences in diversification of Proteaceae in P-impoverished vs. nutrient-rich environments and whether these were linked to adaptations to P-impoverished soils. We explored mature leaf and seed [P] and investigated how these traits changed over the evolutionary history of the family, and within two species-rich genera (Banksia, Hakea). Faster diversification was correlated with lower leaf and higher seed [P] for species-rich genera across the Proteaceae. For Banksia and Hakea, diversification rates peaked at relatively low leaf [P], but not at the lowest leaf [P]. Ancestral state reconstructions indicated that low leaf [P] is a trait that was likely present in the early evolution of the Proteaceae, with recent transitions to higher leaf [P] across several species-poor rainforest genera. Diversification of Proteaceae correlated strongly with P-related traits. In an evolutionary context, functional cluster roots, low leaf [P] and high seed [P] were likely key innovations allowing diversification. Selection for low leaf [P] early in the evolutionary history of Proteaceae pre-adapted ancestors of this family to diversify into oligotrophic environments. We discuss how our findings are likely relevant for understanding diversification dynamics of other plant families that occur in P-impoverished environments.

Nitrogen (N) is often the nutrient limiting the decomposability of shoots from macrophytes in wetlands. We aimed to determine the effects of increasing soil N availability on the decomposition of shoots during the standing-dead phase. We measured the quality of senesced leaves from graminoids and their subsequent aerial decay under different N addition treatments (Control, 0 kg N ha−1 yr.−1; N60, 60 kg N ha−1 yr.−1; N120, 120 kg N ha−1 yr.−1; N240, 240 kg N ha−1 yr.−1) in a temperate marsh. Nitrogen addition increased N concentrations in senesced leaves and often increased phosphorus (P) concentrations. The exponential decay constants (k) of leaves from the N120 and N240 treatments were higher than the control treatment during aerial decay. Nitrogen amounts (in percentage terms) remaining in decaying leaves always significantly decreased after N addition, but the effects on P amounts varied with N addition rates. The nutrient amounts remaining in leaves during the standing-dead phase had negative relationships with the initial nutrient concentrations. Soil N availability exerts remarkable effects on the decay process of standing litters by altering the initial quality, and thus the biogeochemical cycling in temperate wetlands.

Background and aims Strawberry (Fragaria x ananassa) is a high-value crop worldwide. Fusarium oxysporum f. sp. fragariae causes rapid wilting and death of strawberry plants and severe economic losses worldwide. To date, no studies have been conducted to determine colonisation of either susceptible or resistant strawberry plants by F. oxysporum f. sp. fragariae, or whether plant colonisation by F. oxysporum f. sp. fragariae differs between susceptible and resistant cultivars.

Background In plants, the uptake from soil and intercellular transport of inorganic phosphate (Pi) is mediated by the PHT1 family of membrane-spanning proton : Pi symporters. The Arabidopsis thaliana AtPHT1 gene family comprises nine putative high-affinity Pi transporters. While AtPHT1;1 to AtPHT1;4 are involved in Pi acquisition from the rhizosphere, the role of the remaining transporters is less clear. Results Pi uptake and tissue accumulation studies in AtPHT1;8 and AtPHT1;9 knock-out mutants compared to wild-type plants showed that both transporters are involved in the translocation of Pi from the root to the shoot. Upon inactivation of AtPHT1;9, changes in the transcript profiles of several genes that respond to plant phosphorus (P) status indicated a possible role in the regulation of systemic signaling of P status within the plant. Potential genetic interactions were found among PHT1 transporters, as the transcript profile of AtPHT1;5 and AtPHT1;7 was altered in the absence of AtPHT1;8, and the transcript profile of AtPHT1;7 was altered in the Atpht1;9 mutant. These results indicate that AtPHT1;8 and AtPHT1;9 translocate Pi from the root to the shoot, but not from the soil solution into the root. Conclusion AtPHT1;8 and AtPHT1;9 are likely to act sequentially in the interior of the plant during the root-to-shoot translocation of Pi, and play a more complex role in the acclimation of A. thaliana to changes in Pi supply than was previously thought. Electronic supplementary material The online version of this article (doi:10.1186/s12870-014-0334-z) contains supplementary material, which is available to authorized users.

Genes encoding dextranolytic enzymes were isolated from Paenibacillus strains Dex40-8 and Dex50-2. Single, similar but non-identical dex1 genes were isolated from each strain, and a more divergent dex2 gene was isolated from strain Dex50-2. The protein deduced from the Dex40-8 dex1 gene sequence had 716 amino acids, with a predicted M(r) of 80.8 kDa. The proteins deduced from the Dex50-2 dex1 and dex2 gene sequences had 905 and 596 amino acids, with predicted M(r) of 100.1 kDa and 68.3 kDa, respectively. The deduced amino acid sequences of all three dextranolytic proteins had similarity to family 66 glycosyl hydrolases and were predicted to possess cleavable N-terminal signal peptides. Homology searches suggest that the Dex40-8 and Dex50-2 Dex1 proteins have one and two copies, respectively, of a carbohydrate-binding module similar to CBM_4_9 (pfam02018.11). The Dex50-2 Dex2 deduced amino acid sequence had highest sequence similarity to thermotolerant dextranases from thermophilic Paenibacillus strains, while the Dex40-8 and Dex50-2 Dex1 deduced protein sequences formed a distinct sequence clade among the family 66 proteins. Examination of seven Paenibacillus strains, using a polymerase chain reaction-based assay, indicated that multiple family 66 genes are common within this genus. The three recombinant proteins expressed in Escherichia coli possessed dextranolytic activity and were able to convert ethanol-insoluble blue dextran into an ethanol-soluble product, indicating they are endodextranases (EC 3.2.1.11). The reaction catalysed by each enzyme had a distinct temperature and pH dependence.

Thermotolerant Paenibacillus strain Dex70-1B and unidentified strain Dex70-34 produce thermoactive dextran-degrading enzymes. Plasmid-based genomic DNA libraries constructed from mixed bacterial cultures containing Dex70-1B or Dex70-34 were screened for the ability to confer dextranolytic activity at 70 degrees C onto Escherichia coli. One gene, designated dex1, was isolated from each strain. The Dex70-1B and Dex70-34 dex1 gene sequences were non-identical, and encoded proteins containing 597 (M(r) 68.6 kDa) and 600 amino acids (M(r) 69.2 kDa), respectively. The Dex1 amino acid sequences were most similar to one another, and formed a new clade among the family 66 glycosyl hydrolase sequences. Expression of the Dex1 proteins in E. coli produced dextranolytic activity that converted ethanol-insoluble blue dextran into an ethanol-soluble form, suggestive of endodextranases (EC 3.2.1.11). Both enzymes were most active at about 60 degrees C and pH 5.5, and retained more than 70% maximal activity after incubation at 57 degrees C for 9.5 h in the absence of substrate.

The inheritance of chloroplast DNA (cpDNA) in Leucadendron species was studied by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis. A total of 100 progeny from five interspecific crosses involving seven parental species were tested, and all progeny exhibited the cpDNA restriction fragment pattern of the female parent, indicating that cpDNA in Leucadendron is maternally inherited. PCR-RFLP was also employed to study cpDNA variation among 21 Leucadendron species. Parsimony analysis using a heuristic search resulted in a phylogenetic tree that showed limited agreement to the taxonomic classification of Leucadendron species, based on morphological characteristics. The incongruence between cpDNA phylogenetic and taxonomic groupings in Leucadendron may be due to reticulate evolution involving a combination of hybridization and introgression, convergent evolution and/or lineage sorting at the interspecific, intersubsectional and intersectional levels.

Soybean (Glycine max cv. Stevens) suspension cells were used to investigate the expression of the alternative oxidase (Aox) multigene family. Suspension cells displayed very high rates of cyanide-insensitive respiration, but Aox3 was the only isoform detected in untreated cells. Incubation with antimycin A, citrate, salicylic acid or at low temperature (10 °C) specifically induced the accumulation of the Aox1 isoform. Aox2 was not observed under any conditions in the cells. Increases in Aox1 protein correlated with increases in Aox1 mRNA. Treatment of soybean cotyledons with norflurazon also induced expression of Aox1. Reactive oxygen species (ROS) were detected upon incubation of cells with antimycin, salicylic acid or at low temperature, but not during incubation with citrate. Aox1 induction by citrate, but not by antimycin, was prevented by including the protein kinase inhibitor staurosporine in the medium. The results suggest that multiple pathways exist in soybean to regulate expression of Aox genes and that Aox1 specifically is induced by a variety of stress and metabolic conditions via at least two independent signal transduction pathways.

Due to mutation in a single nuclear locus, AEP1, the temperature-conditional pet mutant ts1860 of Saccharomyces cerevisiae fails to synthesize mitochondrial ATP synthase subunit 9 at the restrictive temperature of 36 degrees C. The presence at this temperature of near-normal levels of the cognate oli1 mRNA in mutant ts1860 indicates that, as previously shown, the product of the AEP1 gene is required for translation of the mitochondrial oli1 transcript. In this study the AEP1 gene has been cloned from a wild-type yeast genomic library by genetic complementation of a temperature-conditional aep1 strain at the restrictive temperature. A 2,330-bp genomic fragment which restores subunit 9 synthesis in aep1 mutant strains was characterized. This fragment encoded five open reading frames: the longest of these, at 1,554 nucleotides, was identified as the AEP1 gene, since disruption of this reading frame generated a non-conditional pet strain unable to synthesize subunit 9. The predicted product of AEP1 is a basic, hydrophilic protein of 59,571 Da which possesses a putative mitochondrial address sequence. Hybridization studies with AEP1-specific probes indicate that the gene is located on chromosome XIII and produces several poly(A)+ transcripts ranging in size from 0.9 to 2.7 kb. None of the identified reading frames share significant homologies with entries of several data bases.

The temperature-conditional pet mutant, ts379, of Saccharomyces cerevisiae fails to synthesize mitochondrial ATP synthase subunit 9 at the restrictive temperature due to mutation of a single nuclear locus, AEP2. The inability to synthesize subunit 9 correlates with a lowered accumulation of the cognate oli1 mRNA indicating that the AEP2 product is involved in oli1 transcript maturation or stabilization. The AEP2 gene has been isolated in this study from a wild-type yeast genomic library by genetic complementation of ts379 at the restrictive temperature. A 1,740 nucleotide open-reading frame was observed that encodes a basic, hydrophilic protein of 67,534 Da which possesses a putative mitochondrial address signal. Disruption of chromosomal DNA within this reading frame produced a non-conditional respiratory mutant unable to synthesize subunit 9, identifying the AEP2 gene. Hybridization analyses indicate that AEP2 is located on chromosome XIII and produces a 2.1 kb poly(A)+ transcript. Two additional open-reading frames were found in close proximity to that of AEP2. The three open-reading frames shared no significant homology with entries in several data bases.